Solar control coatings having a layer stack of glass/Si3N4/NiCr/Si3N4 are known in the art, where the metallic NiCr layer is the sole infrared (IR) reflecting layer in the coating.
Unfortunately, while such layer stacks provide efficient solar control and are overall good coatings, they sometimes are lacking in terms of: (a) corrosion resistance to acid (e.g., HCl boil); (b) mechanical performance such as scratch resistance; and/or (c) thermal stability upon heat treatment for tempering, heat bending, or the like (i.e., ΔE* value(s)). For example, a known heat treatable coated article having a layer stack of glass/Si3N4/NiCr/Si3N4 has an undesirably high glass side reflective ΔE* value of above 5.0 after heat treatment (HT) at 625 degrees C. for ten minutes. This high glass side reflective ΔE* value means that the coated article when HT will not approximately match its non-HT counterpart with respect to glass side reflective color.
Accordingly, there exists a need in the art for a coated article that has improved characteristics with respect to (a), (b) and/or (c) compared to a conventional layer stack of glass/Si3N4/NiCr/Si3N4, but which still is capable of acceptable solar control (e.g., blocking a reasonable amount of IR and/or UV radiation) and/or heat treatment.
Commonly owned U.S. patent application Ser. No. 10/338,878 (hereby incorporated herein by reference) discloses a coated article comprising glass/Si3N4/NbN/Si3N4. This coated article is advantageous with respect to the aforesaid glass/Si3N4/NiCr/Si3N4 in terms of color stability upon heat treatment. In particular, coated articles of glass/Si3N4/NbN/Si3N4 described in Ser. No. 10/338,878 may be able to achieve ΔE* values due to heat treatment of less than or equal to 3.0, more preferably less than or equal to 2.5, and so forth.
Unfortunately, while coatings with Nb and NbN IR reflecting layers achieve excellent thermal performance and mechanical durability, their ability to withstand chemical attack is suspect. For example, coated articles of glass/Si3N4/NbN/Si3N4 and glass/Si3N4/Nb/Si3N4 have less than desirable resistance to alkaline attack and oxidation at elevated temperatures.
Thus, it will be appreciated by those skilled in the art that there exists a need for a technique for improving chemical durability of coated articles including Nb inclusive IR reflecting layer(s). In certain other embodiments set forth below, such technique(s) may also be applied to coatings including other types of IR reflecting layers such as Ni or Ni alloy IR reflecting layers.